The present invention relates to electronic coin sorting machines.
Typically, a coin sorting machine includes a decision unit to determine whether a coin is an acceptable specie or an unacceptable slug and a selection unit to sort the species and slugs into separate coin passages. The decision unit includes a coin sensor, such as an inductance coil so that the impedance of the coil changes when a coin passes the sensor. The decision unit further includes circuitry to convert the change in impedance into a change in voltage and frequency to determine whether the coin is a specie or a slug.
FIG. 1 shows a conventional coin sorting machine including coin sensor, or impedance coil, 1 of the decision unit positioned at the side of gradient coin rail, or passage, 2 of the selection unit. A coin introduced through coin inlet 3 passes coin sensor 1 as the coin runs on rail 2. Upon exiting rail 2, a coin passes either into slug passage 4 or specie passage 5 as controlled by coin sensor 1 and gate lever 6. Gate lever 6 is driven by a solenoid (not shown) operating on command from coin sensor 1 to selectively provide a route to slug passage 4 for slugs, upon receiving a slug signal, or a route to specie passage 5 for species.
FIG. 2 shows a signal detection circuit for the selection unit of the coin sorting machine. Coin sensor 1 is incorporated into bridge circuit 7 together with resistor r.sub.0, variable inductor L.sub.1 and variable resistor R.sub.1. Oscillator 8 is connected across bridge circuit 7. Variable inductor L.sub.1 and variable resistor R.sub.1 are adjusted so that bridge circuit 7 is balanced, or establishes an equilibrium, by a change in the impedance of coil 1 only when a specie passes coin sensor 1. Rectifying/smoothing circuit 9 includes differential amplifier 10, rectifiers 11A and 11B and filter condenser 12, and provides rectification and smoothing of output wave form V.sub.B from bridge circuit 7. Voltage divider 13, including resistors 13A and 13B, provides reference voltage V.sub.r at junction 14 to comparator 15. Output V.sub.B from bridge circuit 7 is rectified and smoothed through rectifying/smoothing circuit 9 to produce DC output V.sub.S, which is inputted to comparator 15 to be compared with reference voltage V.sub.r inputted to the comparator 15 from voltage divider 13. The output of comparator 15 is fed into decision circuit 16 which determines whether the coin is a specie or a slug. Circuit 16 includes a flip-flop, a gate and a timer as disclosed, for example, in Japanese Patent Application No. 52-66971 (corresponding to U.S. Pat. No. 4,275,806, entitled COIN SORTING MACHINE, and issued June 30, 1981 to Tanaka et al). Comparator 15 outputs a signal, obtained as the result of comparing reference voltage V.sub.r with output voltage V.sub.S from rectifying/smoothing circuit 9, to decision circuit 16, which makes a decision on whether or not the coin is genuine according to said output signal.
When a specie passes coin sensor 1 in the detection unit, an equilibrium point is established only at one point in the waveform of output V.sub.B from the bridge circuit 7. Consequently, the waveform of output voltage V.sub.S from circuit 9 forms a trough which is lower than reference voltage V.sub.r, only once as shown in FIG. 3(A); and one pulse is sent, as shown in FIG. 3(B), to decision circuit 16. The coin is determined to be a specie in such case. If a slug produces too slow a change in the impedance of coil 1, for example because of a variance in material, size, or weight, an equilibrium point is not established in output waveform V.sub.B from bridge circuit 7. Consequently, a trough lower than reference voltage V.sub.r does not appear in the waveform of output V.sub.S, as shown in FIG. 4(A), and no signal is sent to decision circuit 16, as shown in FIG. 4(B). If a slug produces too fast a change in the impedance of coil 1, two equilibrium points appear in the waveform of output V.sub.B from the bridge circuit 7. Consequently, the waveform of output V.sub.S from circuit 9 forms a W-shaped trough going lower than reference voltage V.sub.r two or more times, as shown in FIG. 5(A), and two or more pulses are sent, as shown in FIG. 5(B), to detector circuit 16.
Therefore, when no pulse is outputted from comparator 15 to decision circuit 16, as shown in FIG. 4(B), and when two pulses are outputted, as shown in FIG. 5(B), decision circuit 16 determines that the coin is a slug and sends a slug signal to the selection unit to route the slug to slug passage 4.
The coin sorting machine as thus far described is generally well-known to those having ordinary skill in the art. However, in conventional coin sorting machines, a slug can produce a W-shaped waveform V.sub.S, as shown in FIGS. 6(A) and 7(A), wherein only one of the two troughs A and B goes below reference voltage V.sub.r. In such a case, only one pulse is inputted to decision circuit 16, which may lead to an erroneous determination that a slug is a specie. Such erroneous determinations seriously reduce the reliability of the coin sorting machine.
It is an object of the present invention to provide an improved coin sorting machine, eliminating the above-mentioned shortcomings and preventing slugs from being erroneously detected as species.